Skewed Pressure Evolution Characteristics Induced By Step-by-step Excavation Of A Double-arch Tunnel And Its Skewed Effect Analysis

The double-arch tunnel has complicated structures and various working procedures.The evolution of surrounding rock pressure and load calculation of double-arch tunnel are very different from those of single tunnel,consequently,the current relevant theories and specifications do not apply in this case.To solve the problem of theoretical research lagging behind engineering practice,it is necessary to do research into the time-space evolution of arching in surrounding rock in the excavation of double-arch tunnel and into the calculation of surrounding rock loads.On the background of the double-arch tunnel project in Huangshan to Quzhou Expressway(in Zhejiang Province),this dissertation,by using a combination of theoretical analysis,laboratory experiment and numerical simulation,presents intensive study on the skewed pressure-arch formation mechanism of the highway double-arch tunnel,morphological evolution of pressure-arch,tunneling load calculation considering skewed effect and the pressure-arch evolution characteristics in saturated strata with fluid-solid coupling effect.The emphases are as follows:Firstly,the inner and outer boundaries of the pressure-arch are identified based on stress analysis of surrounding rock of the double-arch tunnel.In conjunction with the introduced index of strain energy entropy,the geometric configuration,evolution characteristic and skewed effect of the pressure-arch developed in excavating of the double-arch tunnel are presented through numerical simulation.Besides,various factors including sectional dimensions,excavation sequence,lateral pressure coefficient and joint distribution are discussed on how they could affect the evolution of pressure-arch.Secondly,according to the above-obtained pressure-arch geometry,a new method is proposed for calculation of surrounding rock loads with special consideration on the skewed effect of surrounding rock pressure,which extends the Protodyakonov's theory and the current design method.The effects of stress conditions and excavating sequences are also analyzed.Thirdly,the simulated experiment with analogy material and infrared thermal imaging technique are combined to conduct uniaxial compression of cylinder model and circle tunnel model,and also to conduct staged excavation of the double-arch tunnel.The dynamic evoluting of the arching process in double-arch tunnel excavation are comprehensive analyzed both from meso-structural property of the analogy material and macro-deformation of the surrounding rock.Moreover,the infrared characteristic of the analogy material and the consistency of infrared temperature and stress response are investigated.Finally,double-arch tunneling in water-rich strata are studied by using fluid-solid coupling analysis method on the basis of the foregoing work,which reveals the fluid-solid coupling effects on pressure-arch configuration and arching process.In addition,influence of various buried depths,excavating methods and permeability coefficients of surrounding rock are investigated through parameter sensitivity analysis.